INTERPRETATIONS AND CONCLUSIONS 145 



examination of the formations themselves. It is on account of this 

 complexity of the proofs and the varying opinions as to both the value 

 and the inferences regarding contemporaneity to be drawn from any or 

 all the visible evidence supplied by the formations as geologic units that 

 leads me to a conviction that we must dispense with any association of 

 time with the definition of a stratigraphic formation, and use, in dis- 

 criminating, defining, and classifying them, only those marks which are 

 visible and can be measured, located, and described in scientific terms. 



In all such cases as in the one cited the facts are stated, when it is 

 said that correlation with the Devonian system is recognized in the Vir- 

 ginia formations, Monterey, Romney, Jennings, and Hampshire, that 

 their division is recognized in the Virginia region on a basis of lithologic 

 difference, and that the homotaxial relations of these formations, roughly 

 speaking, correspond to the Oriskany, Hamilton, Chemung, and Catskill 

 of the New York classification. It is misleading, however, to speak of 

 the several pairs of formations as " chronologic equivalents." The evi- 

 dence is not in hand to prove that they are or are not; their chronologic 

 relations are still to be established. 



If any of the fossils occurring in the Hamilton formation, as defined 

 in central New York, were strictly confined in their vertical range to the 

 limits marking the base and the top of the portion of the section de- 

 scribed as Hamilton, the case would be different. In such a case it 

 would be possible to infer that the same fossils elsewhere could be inter- 

 preted into contemporaneity of sedimentation. But the facts accumu- 

 lated disprove such an assumption ; and until the total stratigraphic 

 range for fossils is ascertained for each area of distribution, and the 

 question as to whether that range is different in separate regions is estab- 

 lished, fossils can not be used as proof of the contemporaneity of short 

 sections of the stratigraphic column which happen locally to hold the 

 same species. 



Geological Usage of Term Fauna 



A word may be added to explain the geological usage of the term 

 fauna. 



In literature there has grown up from the old conception of separate 

 creations and the peopling of the earth with separate organism at the 

 beginning of each geological period the idea that the fossils found in a 

 formation are peculiar to the formation — are " leit fossilien." Thus the 

 time when a formation was formed and the fossils contained in the 

 formation have come to be regarded as correlative terms. The time 

 scale is thus regarded as only another mode of indicating the strati- 



XX— Boll. Geoi,. Soc. Am., Vol. 16, 1904 



